For now I'm not calling this a guide as I'm still learning and experimenting myself, it's more of a note taking place for myself. However others of course may look at my notes and comment in if they wish.

Steps to Export from 3ds Max into IMVU using FBXVersion of 3ds Max used: 2016

Mesh, Animation , Morph and Skeleton Preparation

Example Stack

Mesh
Your geometry must be an Editable Mesh or Editable Poly
If your geometry is a Deformable GPoly or Editable Patch, the Skin and Morph may be lost (usually just the morph)
Physique may not work ?

Skeleton
Note: CAT Bones seem to be a struggle for some versions of Max to export

Animation
Just have an animation I guess?

Morph
There is no longer a need to link your morph targets to your base mesh. This is an obsolete step.
Also I have currently not once reset the Xform either. I believe this to be an obsolete step as well.
Simply have a Morpher Modifier on your stack with loaded morph targets

To any Mesh Head makers. You will absolutely want to use FBX to create your heads.

Currently, exporting the actual .XPF separate using IMVU exporters actually will work with your FBX mesh.

Export or Export Selected

Note: It does not matter what frame you export on!

I prefer Export Selected because the Export option will normally throw errors due to the default avatar's skeleton and it typically takes a bit longer to export. However, the errors it throws in a lot of cases are irrelevant.

Export Selected
To use this, you must select EVERYTHING you wish to export. If it's not selected, it's not getting exported. Very quick to export. Any errors thrown should be read.I exported a 100 Morph Target Mesh in a little over a second.

Export
This will simply export everything, making the FBX rather large, time consuming to export, and IMVU itself takes awhile to read the file. Will most likely throw a lot of errors, as the Default File contains many things the FBX export doesn't like.

Convert Deforming Dummies to Bones
Check this if you are trying to use Dummy Nodes as bones

Triangulate
I believe this isn't needed

Preserve Edge Orientation
???

Animation

Animation
To export Animations, Morphs, Meshes, you must check this.

Use Scene Name
Will name your Animation and Morph file names in IMVU to the name of your 3ds Max file

Remove Single Key
???

Bake Animation
Check if you want to record skeletal animation

Start/Stop
The time in which it will record the keyframes

Step
1 Step will record a keyframe every single keyframe
2 Steps will record a keyframe every other keyframe
3 Steps will record a keyframe every 3 keyframes
and so on...

Resample All
Very important
It's hard to explain what this does as I don't know fully myself, but usually it would seem you want this checked. Here's an example of it at work, but I know it does much more than just this.

I have a small question though and hope this is me doing some silly mistake, when I export earrings for example (and it doesnt matter if I select the femalemaster/selection only or head), they always appear beside the avatar floating even though the asigned attachment node is the Head.

Any ideas what could be wrong, did I miss a step or is it the exporter?

There's a lot of reasons really and being new to it myself, I can't really name the reasons why yet. I'm going to try and make a video soon of exporting simple accessories, animated, and clothing. Hopefully it will help.